1. Field of the Invention
The present invention relates to a nanostructure material, and in particular relates to a nanostructure material with metallic oxide serving as detecting material for a gas detector.
2. Description of the Related Art
Monitoring and controlling micro contaminants, is one of the most important issues for IC manufactures, as critical dimensions continue to shrink.
International Technology Roadmap for Semiconductor (ITRS) predicts that the critical dimensions of a chip scale will shrink to 32 nm in 2013. Thus, controlling micro contaminants is critical for IC manufacturers. For example, for 32 nm semiconductor processes, a recommended sensitive area micro contaminants (such as acid, base, organic compounds or dopants) value for a clean room is less than 10 ppt to 150 ppt. Therefore, a gas sensor having a low detection limit is needed, to assure that the air quality in a clean room meets advanced semiconductor process requirements.
Commonly used gases and its by-products during the IC fabrication process can be classified into: flammable gas, such as silicon methane, methane or the likes; toxic gas, such as arsine, diborane, phosphine or the likes; corrosive gas, such as hydrogen fluoride, hydrogen chloride or the likes; and greenhouse gas, such as tetrafluoromethane, nitrogen trifluoride or the likes, depending on their chemical properties and influences. These toxic, hazardous gases may be produced during a thin film, chemical vapor deposition, dry etching, diffusion, ion implantation and epitaxy process.
Phosphine is a colorless gas, when in a room temperature environment. It has a nauseating garlic smell and is toxic. Breathing in phosphine by humans, can cause difficulty in breathing, which may lead to death. Furthermore, phosphine is also dangerous because it is a flammable gas having explosion limits between 1.6% and 98%. However, phosphine is often used as an N-type dopant which is doped into polysilicon by diffusion or ion implantation. Therefore, phosphine gas sensors must be installed in semiconductor foundries in accordance with legal requirements
At present, commercial phosphine gas sensors are mainly classified into electrochemical detectors and ribbon detectors, which dominate over 90% of the phosphine gas sensor market. The detection limit of commercial phosphine gas sensors is about 100 ppb in accordance with law, which is 1,000-10,000 times greater than the recommended value by the ITRS. Meanwhile, it is easy for other gases to interfere with the commercial phosphine gas sensors. Thus, in order to address the above problems, the current detection methods that foundries use is traditional sampling and analysis. The method includes exposing chips to the clean room atmosphere for 24-48 hours, bringing the contaminants deposited on the chip surface to an acidic solution by concentrated HF acid, and analyzing the contaminants by using inductively coupled plasma mass spectrometry (ICP-MASS). However, a lot of time, labor and materials are required for the method, and real-time detection is not accomplished; thereby lowering fabrication yields.
Other phosphorus-containing molecules, such as a phosphorusic acid, are corrosive for the eyes, skin, and respiratory tract of humans, and may cause blindness and permanent injuries. Phosphorusic acid may decompose to toxic phosphorus oxides. Therefore, phosphorusic acid is hazardous for humans.
Accordingly, a novel material and technique for detecting phosphorus-containing compounds is desired to address the described problems.